Crystal structure of bis{3-(3-bromo-4-methoxyphenyl)-5-[6-(1H-pyrazol-1-yl)pyridin-2-yl]-1,2,4-triazol-3-ato}iron(II) methanol disolvate

The title charge-neutral complex is a low-spin complex with a moderately distorted pseudo-octahedral coordination environment of the metal ion. As a result of their asymmetric shape, the molecules stack into chains, which eventually pack into layers and, finally, into a three-dimensional network connected by weak C—H⋯N, C—H⋯C hydrogen bonds and C—H⋯π interactions.


Chemical context
A broad class of coordination compounds exhibiting spin-state switching between low-(total spin S = 0) and high-spin states (total spin S = 2) is represented by Fe II complexes based on tridentate bisazolepyridine ligands (Halcrow, 2014;Suryadevara et al., 2022;Halcrow et al., 2019). In the case of asymmetric ligand design, where one of the azole groups carries a hydrogen on a nitrogen heteroatom and acts as a Brønsted acid, deprotonation can produce neutral complexes that can be either high-spin (Schä fer et al., 2013) or low-spin (Shiga et al., 2019) or exhibit temperature-induced transitions between the spin states of the central atom (Seredyuk et al., 2014), depending on the ligand field strength. The periphery of the molecule, i.e. ligand substituents, also plays an important role in the behaviour, determining the way in which molecules are packed in the lattice and their interactions with each other, and therefore further influencing the spin state adopted by the central atom. As we have recently demonstrated, the dynamic rearrangement of the methoxy group between the bent and extended configurations can lead to a highly hysteretic spin transition via a supramolecular blocking mechanism (Seredyuk et al., 2022).

Structural commentary
The title complex has a asymmetric molecule with divergent phenyl groups. The ligand molecules are almost planar (r.m.s. deviation = 0.330 Å ), including the methoxy substituents, which also lie in the plane of the aromatic groups [atoms C17 and C35 are 0.514 (1) and 0.116 (1) Å , respectively, away from the planes passing through their respective ligand molecules]. The two independent methanol molecules form O-HÁ Á ÁN hydrogen bonds with the triazole (trz) rings of the ligand molecules ( Fig. 1, Table 1). The central Fe II ion of the complex has a distorted octahedral N 6 coordination environment formed by the nitrogen donor atoms of two tridentate ligands (Fig. 1).
The average bond length, <Fe-N> = 1.949 Å , is typical for low-spin complexes with an N 6 coordination environment (Gü tlich & Goodwin, 2004). The average trigonal distortion parameters AE = AE 1 12 (|90 À ' i |), where ' i is the angle N-Fe-N 0 (Drew et al., 1995), and Â = AE 1 24 (|60 À i |), where i is the angle generated by superposition of two opposite faces of an octahedron (Chang et al., 1990) are 93.3 and 298.8 , respectively. The values reveal a deviation of the coordination environment from an ideal octahedron (where AE = Â = 0) but is, however, in the expected range for bisazolepyridines and similar ligands (see below). The calculated continuous shape measure (CShM) value relative to the ideal O h symmetry is 2.24 (Kershaw Cook et al., 2015). The volume of the [FeN 6 ] coordination polyhedron is 9.536 Å 3 .

Supramolecular features
As a result of their asymmetric shape, neighbouring complex molecules fit into each other and interact through a weak C-H(pz)Á Á Á(ph) intermolecular contact between the pyrazole (pz) and phenyl (ph) groups respectively (Table 1). The monoperiodic supramolecular chains formed extend along the c-axis direction with a stacking periodicity of 10.6434 (3) Å (equal to cell parameter c; Fig. 2a). Through weak intermolecular C-H(pz, py)Á Á Á N/C(pz, trz) interactions in the range 3.128 (14)-3.734 (11) Å (Table 1), neighbouring chains are linked into corrugated layers in the bc plane (Fig. 2b,c). The layers stack with interlayer interactions limited to C-HÁ Á ÁN(trz) and C-HÁ Á Á(ph) contacts involving the methyl groups (Fig. 2c). The voids between the layers are occupied by methanol molecules, which also participate in bonding between neighbouring layers (see Table 1 for the complete list of intermolecular interactions).
CrystalExplorer (Spackman et al., 2021), with a standard resolution of the three-dimensional d norm surfaces plotted over a fixed colour scale of À0.2869 (red) to 2.4335 (blue) a.u. (Fig. 3). The pale-red spots represent short contacts and negative d norm values on the surface corresponding to the interactions described above. The overall two-dimensional fingerprint plot is illustrated in Fig. 4      from HÁ Á ÁH interactions, which are located in the middle region of the fingerprint plot. HÁ Á ÁC/CÁ Á ÁH contacts contribute 25.2%, and the HÁ Á ÁBr/BrÁ Á ÁH contacts contribute 13.2% to the Hirshfeld surface and both result in a pair of characteristic wings. The HÁ Á ÁN/NÁ Á ÁH contacts, represented by a pair of sharp spikes in the fingerprint plot, make a 12.2% contribution to the Hirshfeld surface. Finally, HÁ Á ÁO/OÁ Á ÁH contacts, which account for 4.0% of the contribution, are mostly distributed in the middle part of the plot.

Energy framework analysis
The energy framework (Spackman et al., 2021), calculated using the wave function at the HF/3-21G theory level, including the electrostatic potential forces (E ele ), the dispersion forces (E dis ) and the total energy diagrams (E tot ), are shown in Fig. 5. The cylindrical radii, adjusted to the same scale factor of 100, are proportional to the relative strength of the corresponding energies. The major contribution to the intermolecular interactions is due to the dispersion forces (E dis ), reflecting the dominating interactions in the lattice of the neutral asymmetric molecules. The topology of the energy framework resembles the topology of the interactions within and between the layers described above. The calculated values E tot are in the range 65.2-87.6 kJ mol À1 for intrachain and intralayer interactions, whereas for the interlayer interactions they are within 7.7-23.4 kJ mol À1 . The colour-coded interaction mappings within a radius of 3.8 Å of a central reference molecule for the title compound together with full details of the various contributions to the total energy (E tot ) are given in the supporting information.

Database survey
A search of the Cambridge Structural Database (CSD, Version 5.42, last update February 2021; Groom et al., 2016) reveals several similar neutral Fe II complexes with a deprotonable azole group, for example, derivatives of a pyrazolepyridine-tetrazole (IGERIX and LUTGEO; Gentili et al., 2015;Senthil Kumar et al., 2015) and a pyrazole-pyridinebenzimidazole (XODCEB; Shiga et al., 2019). There are also related complexes based on phenanthroline-tetrazole, such as QIDJET (Zhang et al., 2007) and phenanthroline-benzimidazole (DOMQUT; Seredyuk et al., 2014). Schematic structures of the complexes are shown in Fig. S1 in the supporting information. The Fe-N distances of these complexes in the low-spin state are 1.933-1.959 Å , while in the high-spin state they are in the range 2.179-2.184 Å . The values of the trigonal distortion and CShM(O h ) change correspondingly, and in the low-spin state they are systematically lower than in the highspin state. Table 2 collates the structural parameters of the complexes and of the title compound.

Refinement
Crystal data, data collection and structure refinement details are summarized in

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.